IT was the defining moment of their careers, as the woman who would become one of the most famous faces in history wore the dress they had designed as she walked down the aisle.

As Prince Charles married Lady Diana Spencer at St Paul's Cathedral, the eyes of the world were on the sumptuous ivory taffeta and antique lace dress - with a 25-metre train - designed by husband and wife David and Elizabeth Emanuel.

After 25 years of stubbornly refusing to reveal the behind the scenes details of the build-up to the wedding, the Emanuels have agreed to put pen - and pictures - to paper.

But unlike Diana's former butler, the couple - who are no longer married - say they are not out to shock.

When Paul Burrell released his book proclaiming secrets about Diana and her life, David Emanuel said he was "horrified" and called it "a scandal". He said, "The poor lady has died and she cannot defend herself. Unfortunately she is in a position where anyone can say anything about her."

But the Bridgend-born designer says his book will be more a pictorial celebration of the run-up to her wedding.

After years of fielding questions from a public intrigued by the late Princess, the designer said the time was right to tell the story.

He said yesterday, "It is a really lovely book that is about the making of her dress with anecdotes about that time.

"It is certainly not in any way anything scandalous. There isn't anything like that."

A Dress For Diana, which was co-written with Emanuel's ex-wife Elizabeth, brings together images of the dress and bridesmaid's dresses and the personal diaries and letters from the designers which were written at the time.

This is the first time the Emanuels have revealed the story of one of the world's most famous dresses and the secrets about the transformation of Diana into the fairy-tale Princess.

Coinciding with the 25th anniversary of Diana's wedding to Prince Charles, the book will be released in August and David said it was a timely celebration.

"I travel the world with my show Shop the World and people have never stopped asking about Diana. They ask me what was she really like," said David, who was heading to Milan yesterday.

"And it was mounting up with museums across the world who would ring up and ask if we had items to display.

"There is a story here, and there are a lot of fans all over the world so we thought to do it once and for all and finally close that chapter."

After Diana's wedding day the Emanuels packed every bit of fabric, pearl and sequin into trunks and secured them in a bank vault. And despite the 25ft train, there seems to have been plenty of material left on the cutting room floor.

David says that there are definitely enough items to make a museum exhibition. However that is not on the cards.

The designer, who is working on a special wedding collection for OK magazine, said the trunks in the bank vault had been untouched for decades - until now.

"After her wedding day we packed and tucked everything away not knowing what to do with them," said David yesterday.

"As you can imagine, it was very emotional going through them and it brought back all the stories from her wedding."

Some of these stories have made their way into the book which the Emanuels have just finished penning.

They promise to reveal the identities of people behind secret codes like "B.P" and "Debra", royal formality and security procedures. And the design duo reveal the levels of madness that occurred to keep the final design a secret.

"We are looking at this book as a lovely memento piece with some personal shots that I took as well at the time," he added.